1. Field
Exemplary embodiments of the present invention relate to an etching composition, and more particularly, to a high-selectivity etching composition capable of selectively removing a nitride film while minimizing the etch rate of an oxide film and to a method for fabricating a semiconductor, which includes an etching process employing the etching composition.
2. Description of the Related Art
In semiconductor fabrication processes, oxide films such as a silicon oxide film (SiO2) and nitride films such as a silicon nitride film (SiNx) are typically used as insulating films. These oxide and nitride films may be used alone or stacked alternately with each other. In addition, these oxide and nitride films are used as hard masks for conductive patterns such as metal interconnects.
In a wet-etching process for removing nitride films, a mixture of phosphoric acid and deionized water is generally used. Deionized water is used to prevent a decrease in the etch rate of the nitride film and a change in the etching selectivity of the nitride films with respect to oxide films. However, even when the amount of deionized water changes minutely, a failure occurs in the nitride film etching process. Phosphoric acid, one of strong acids, is corrosive, and thus difficult to handle.
In an attempt to solve these problems, a technology of removing a nitride film using an etching composition comprising hydrofluoric acid (HF) and phosphoric acid (H3PO4) or nitric acid (HNO3) and phosphoric acid (H3PO4) was suggested, but resulted in a decrease in the etching selectivity for a nitride film with respect to an oxide film. In addition, a technology of removing a nitride film using an etching composition comprising phosphoric acid and silicate or phosphoric acid and silicic acid was also suggested, but silicate or silicic acid is not suitable for use in semiconductor fabrication processes, because it causes generation of particles that may affect a substrate.
FIGS. 1a and 1b are cross-sectional views showing a device isolation process for a flash memory device.
As shown in FIG. 1a, a tunnel oxide film 11, a polysilicon film 12, a buffer oxide film 13 and a pad nitride film 14 are sequentially formed on a substrate 10. Subsequently, the polysilicon film 12, the buffer oxide film 13 and the pad nitride film 14 are selectively etched to form trenches. Then, a SOD oxide film 15 is formed so as to gap-fill the trench. A CMP process is then performed on the SOD oxide film 15, using the pad nitride film 14 as a polishing stop film.
Then, as shown in FIG. 1b, the pad nitride film 14 is removed by wet-etching with a phosphoric acid solution, and the buffer oxide film 13 is removed by a cleaning process. Thus, a device isolation film 15A is formed in a field region. However, when phosphoric acid is used in this process for removing the pad nitride film 14, not only the pad nitride film 14 but also the SOD oxide film 15 are etched due to a decrease in the etching selectivity for the nitride film with respect to the oxide film, which may make it difficult to control the effective field oxide height (EFH). Thus, a wet-etching time sufficient for removal of the nitride film may not be ensured, or an additional process is required, which results in changes that adversely affect the device characteristics.
Accordingly, there is a need for a high-selectivity etching composition that may selectively etches nitride films with respect to oxide films and, at the same time, does not cause problems such as particle generation.